Fix versioning on stable Fedora

MR 1735 indicate HEAD state in tarball/rpm name added a git tag to builds when VERSION_ON_UPSTREAM=0. While this will never impact Fedora rawhide because the os-build tree here always has VERSION_ON_UPSTREAM=1, it does impact stable Fedora branches where this is set to 0. Until I can think of a more clever way to handle this, let's just restrict it to ifneq ("$(DISTRO)", "fedora"). Tested in the fedora-5.18 branch.

Signed-off-by: Justin M. Forbes jforbes@fedoraproject.org